Principles of Aerial Photography

Aerial Survey

A general term meaning the collection of information conducted from an airborne platform. Information can be collected from various remote-sensing sensors such as film and digital cameras, thermal, multispectral and hyperspectral sensors, and LiDAR.

Oblique Photography

Aerial photographs with more than 3 degrees of tilt are considered oblique. There are two basic types of oblique aerial photography.

High angle oblique – the apparent horizon is shown.

Low angle oblique – the apparent horizon is not shown.

Obliques are used for visualization and illustration purposes as measurements extracted are not accurate due to very large distortions.

Aerial Photogrammetry

The science of obtaining accurate geometric measurements using aerial photographs. It includes aerotriangulation, or block adjustment, of up to 1000s of photographs using point of common detail and airborne GPS. Aerotriangulated stereo images is the 3D base product from which a number of 2D and 3D products are derived, such as DEMs.

Orthophotography

Orthophotos are generated from overlapping vertical aerial photographs and processed to remove perspective and the effect of the terrain.

Orthophoto process geometrically “corrects” a vertical aerial photograph into the equivalent of a traditional map. It retains the advantages of a photograph, visually displaying actual cultural and land features, rather than representing those features using symbols and lines.

In other words it is a virtual photograph as if taken from an infinite distance, looking straight down.

Topographic Maps

Topographic maps are typically used in planning infrastructure and resource management. The information conveyed in this type of map can include contour lines, spot elevations, hydro-enforced breaklines, and other required elevation data. To develop topographic maps photogrammetric methods are used to interpret aerial photography, LiDAR data sets, and other remote sensing data.

LiDAR

LiDAR (Light Detection and Ranging) is mapping technology that determines distance to an object or surface using laser pulses to measure elevation, providing great accuracy and detail. LiDAR data is directly processed to produce detailed bare earth models in a variety of formats.

LiDAR technology offers one of the most accurate, expedient and cost-effective ways to capture elevation information.

Digital Elevation Models (DEMs)

Represents the terrain elevations on the earth’s surface using a collection of discrete elevation points at regularly spaced intervals..

Digital Terrain Model (DTM)

A DTM is a DEM in which terrain data has been further enhanced with breaklines, creating greater accuracy as it contains additional information defining terrain.

Mapping

Mapping provides great accuracy, allowing for features to be represented in full detail — with the level of accuracy being carefully tailored to meet each clients’ project needs.

Corridor Mapping

Mapping is useful for transportation routes, high voltage transmission lines, and pipeline routes. Final deliverables can include orthophotography, allowing the entire corridor to be visualized in great detail, as well as topographic maps and planimetric maps of proposed vertical and horizontal alignments and final routes.

Planimetric maps show only the horizontal position of features on the Earth’s surface which reveal geographic objects, natural and cultural physical features, and entities in their true coordinate positions, depicting them to scale without topographic properties. These features include: road edges and centerlines, culverts, water and storm drainage features, utility access covers, utility poles, signs, fences, and vegetation.